The present invention relates to fluid piping systems and more particularly to piping systems of the type wherein a metallic housing is lined with a non-metallic material selected from the group consisting of elastomers and plastomers.
Piping systems are in use wherein metal pipe sections or spools are lined with a layer of corrosion resistant plastic. Generally, connections are made between sections of such pipe by flange joints, in which case the lining is brought out of the pipe and flared over the face of the flange both to protect the metal from the fluids being carried and to serve as a gasket. While we shall speak herein of a flange face it should be understood that we intend to include any surface to which a mating flange can be bolted or otherwise secured. An example is a vessel with a flange connector that might not literally fall within the definition of a flange.
Unfortunately, the flared liners cause the mechanical integrity of the flange connections, and consequently the integrity of the entire system, to be degraded. Because the materials used for liners have low strength within their service temperature range, bolting loads must be low. Such bolt loads are significantly less than encountered in conventional unlined piping systems; therefore, worker skill, worker attitude, and pipe misalignment become critical factors. Cold-flow as well as hot-flow of these non-metallic materials cause loss of bolt torque from the already low installation torque. Therefore, such known pipe connections suffer from various types of failure in use.
Beyond normal service conditions, aggravating factors are occasionally encountered that further degrade the integrity of the connection. For example, abnormal operating conditions such as: over-temperature, over-pressure, vibration and water hammer; and abnormal environmental conditions such as: wind, flood, ground settling, earthquake and vehicle impact; either alone or in combination, cause additional deterioration of the original gasket compression and bolting pre-load.
Finally, the fire resistance of the lined system, which should be high because of the metal housings, is compromised by the total vulnerability of the flared ends of the liner.